The present invention relates to a connecting rod made of composite material, especially for internal-combustion engines, as well as to a method for manufacturing such a connecting rod.
Such a connecting rod is an elongate component which includes, in addition to a central shank, a wider big end, which is the part of the connecting rod lying on the crankshaft side, and a narrower small end, which is the part of the connecting rod lying on the piston side. In order to mount it, the big end must be able to open, and it therefore includes two elements fastened by two bolts which exert a significant stress on that surface of the element against which they are tightened. The connecting rod is a component which has a preferential direction of loading and has to have a high stiffness preventing deformations around the bores of the small end and the big end.
A connecting rod made of composite material is already known, for example from Patent FR-A-2,654,483. By composite material is meant a material which includes a reinforcement of yarns or fibers, this reinforcement being embedded in a matrix of cured synthetic material. Such a composite material, in addition to the weight saving that it provides, withstands mechanical loads extremely well, has a high corrosion resistance and excellent high-temperature behavior. However, in Patent FR-A-2,654,483, these properties of composite materials are not fully exploited on account of the fact that, in this case, the shank, small end and big end of the connecting rod are produced in the form of separate components connected by adhesive bonding and winding of a yarn, forming a strap. Furthermore, such a production is complicated and has to be implemented in several steps, thereby preventing effective mass production of such connecting rods.
The object of the present invention is to avoid these drawbacks and relates to a connecting rod made of composite material, the structure of which makes it possible, on the one hand, to fully exploit the properties of the composite materials and, on the other hand, to manufacture a large number of such components easily and quickly.
For this purpose, the connecting rod made of composite material, especially for internal-combustion engines, said composite material being formed by a reinforcement embedded in a cured material, and said connecting rod comprising, along the longitudinal extension of the connecting rod, a central shank extended respectively, at its two extremities, by a connecting-rod big end and a connecting-rod small end, is noteworthy in that, according to the invention, said connecting rod is produced entirely as a single component made of composite material, in that the reinforcement of said composite material comprises superposed plies of crossed straight filling yarns, the filling yarns, which extend parallel to the longitudinal extension of the connecting rod, constituting at least twice the volume percentage of the filling yarns which extend in each of the directions other than the longitudinal extension of the connecting rod and in that binding yarns pass through said superposed plies.
Thus, the reinforcement of the connecting rod made of composite material according to the invention has an increased strength in the maximum load direction, that is to say the longitudinal extension of the connecting rod, and, in addition, since the connecting rod is made of a single component of composite material, it is simple to manufacture and the properties of the composite material may be exploited to the maximum.
Advantageously, assuming that the filling yarns of the reinforcement extending parallel to the longitudinal extension of the connecting rod are the 0xc2x0 direction yarns, the other filling yarns of the reinforcement extend along the 45xc2x0, 90xc2x0 and 135xc2x0 directions.
In particular, the reinforcement may comprise as many 0xc2x0 direction filling yarns as there are filling yarns extending along the other three, 45, 90xc2x0 and 135xc2x0, directions.
Preferably, with respect to the total volume of the composite material including the reinforcement and the cured matrix, the volume percentage of the filling yarns is between 40% and 40% and the volume percentage of the binding yarns is between 1% and 10%.
In particular, the volume percentage of the 0xc2x0 direction filling yarns is at least substantially equal to 27%, while the volume percentage of the 45xc2x0, 90xc2x0 and 135xc2x0 direction filling yarns is at least substantially equal, in each case, to 9%.
Moreover, the volume percentage of the binding yarns may be at least substantially equal to 3%.
Advantageously, for each series of plies, the filling yarns are arranged in the following sequence: 0xc2x0 direction yarns, 45xc2x0 direction yarns, 0xc2x0 direction yarns, 90xc2x0 direction yarns, 0xc2x0 direction yarns and 135xc2x0 direction yarns.
According to another characteristic of the invention, additional 90xc2x0 direction filling yarns are provided in the region of the connecting-rod big end, increasing its thickness.
Preferably, said additional 90xc2x0 direction filling yarns are incorporated in each of said series of plies.
According to yet other characteristics of the invention, 0xc2x0 direction filling yarns, going around the connecting-rod small end, may be incorporated between said series of plies, and/or yarns, going around the connecting-rod small end, may be arranged by stitching along the edges of said connecting-rod small end.
The present invention also relates to a method for manufacturing a connecting rod made of composite material, which has just been described, noteworthy in that, according to the invention:
a) a reinforcement for a sheet of composite material is produced, said reinforcement comprising superposed plies of crossed straight filling yarns, the filling yarns, which extend parallel to a first direction, constituting at least twice the volume percentage of the filling yarns which extend in each of the other directions, and binding yarns passing through said superposed plies;
b) said reinforcement is impregnated with a synthetic material intended to form the matrix of said sheet of composite material;
c) said synthetic resin is cured so as to form said sheet of composite material;
d) said sheet of composite material is cut so as to obtain connecting-rod preforms, said first direction corresponding to the longitudinal extension of said preforms; and
e) each connecting-rod preform thus obtained is machined into its final state.
In particular, assuming that the filling yarns of the reinforcement extending along said first direction are the 0xc2x0 direction yarns, the other filling yarns of the reinforcement extend along the 45xc2x0, 90xc2x0 and 135xc2x0 directions.
Preferably, in step a), as many 0xc2x0 direction filling yarns are laid down as there are filling yarns extending along the other three, 45xc2x0, 90xc2x0 and 135xc2x0, directions.
Advantageously, for each series of plies, the filling yarns are laid down according to the following sequence: 0xc2x0 direction yarns, 45xc2x0 direction yarns, 0xc2x0 direction yarns, 90xc2x0 direction yarns, 0xc2x0 direction yarns and 135xc2x0 direction yarns.
According to another characteristic of the invention, in step a), additional 90xc2x0 direction filling yarns are laid down in the region corresponding to the connecting-rod big ends.
Preferably, in this case, said additional 90xc2x0 direction filling yarns are laid down at the time of production of each of said series of plies.
According to yet another characteristic of the invention, between said series of plies, 0xc2x0 direction filling yarns, going around the places provided for the connecting-rod small ends, are laid down.
In particular, step d) may be carried out before steps b) and c) in order thus to make it possible, after step d), to stitch yarns into the reinforcement, going around the connecting-rod small end, along the edges of the latter.